[Ultrastructural subclassification of undifferentiated carcinomas of the parotid gland (author's transl)].

Eleven undifferentiated carcinomas of the parotid gland which could not be classified to a special type of carcinoma based on their histological and cytological structure were analysed ultrastructurally and compared with the ultranstructural cytodifferentiation during the development of the human parotid gland. The study had the following results: 1. The tumors were composed of partly solid, moderately clear cell formations, partly trabecular cell groups with hyaline stroma light microscopically. 2. Five cell types could be distinguished ultrastructurally: undifferentiated epithelial cells (clear cytoplasm, with or without glycogen deposits, few cell organelles, occasionally cilias), undifferentiated duct cells (middle content of organelles, primitive secretion products, indented cell membranes), secretoric active epithelial cells (distinct content of organelles, microtubules, secretory granules), epidermoid cells (desmosomes, tonofibrils) and myoepithelial cells (myofilaments, spindle-shaped cell nuclei, abundant content of organelles). 3. Seven of the 11 undifferentiated carcinomas were constructed either only of epidermoid cells or additionally of undifferentiated duct cells or secretoric active epidelial cells. These tumors were therefore classified as undifferentiated epidermoid carcinomas. 4. Four of the 11 undifferentiated carcinomas were constructed of myoepithelial cells in combination with epidermoid cells and undifferentiated duct or epithelial cells. These tumours were classified as undifferentiated salivary duct carcinomas. 5. Homogeneous cell types — except the epidermoid cells — are found in the embryonal development of the human parotid gland. From this fact the conclusion is derived that the salivary duct system is considered as a tumoral matrix. 6. The basal reserve cells of the salivary duct system are a pluripotent cell material with different lines of differentiation including the epidermoid cells.